The present invention relates to a cleaning device for removing residual developer particles from a photoconductive element of an electrographic copier or printer. More particularly, the present invention relates to a cleaning device in the form of a screen mesh or grille for removing residual developer particles from a photoconductive element of an electrographic printer or copier.
In the process of electrophotographic or xerographic printing, a photoconductive member is employed to record an image. The photoconductive member, which may typically take the form of a belt or a drum, is charged to a substantially uniform potential to sensitize its surface. In the case of a copying machine, the charged portion of the photoconductive surface is exposed to a reflected light image of an original document to be reproduced. The light image is recorded as an electrostatic latent image on the photoconductive member corresponding to the informational areas contained on the original document.
In the case of a printer connected to a computer, a similar process is used to record information on the photoconductive member. The charged portion of the photoconductive surface is exposed to a light image, the shape of which is controlled by input signals from the computer. For example, a laser or an LED array receiving input signals from the computer functions as an optical print head and illuminates the photoconductive member with a light image of a particular shape. Here too, an electrostatic latent image corresponding to desired informational areas is recorded on the photoconductive member.
After recording the electrostatic latent image o the photoconductive member, the latent image is developed by bringing a developer material or toner into contact with it. The developer material is attracted to the electrostatic latent image and forms a powder image on the photoconductive member corresponding to the electrostatic latent image. The powder image is subsequently transferred to a sheet of recording medium, such as a sheet of paper. Thereafter, the powder image is permanently affixed to the sheet in image configuration by a variety of methods, such as by fusing.
The above-mentioned operations may be carried out by arranging a number of stations in sequence about the photoconductive member. Thus, the photoconductive member is usually surrounded in sequence by a charging station, an imaging station, a developing station, and a transfer station. A discharging station and a cleaning station are also arranged about the photoconductive member to ready it for use again.
As used herein, the term "electrographic printing apparatus" and the like are intended to include both copying and printing machines. Such machines include a developer unit operative to deliver toner with or without a carrier to the photoconductive member. Typically the toner is stored in a hopper where it is mixed with a suitable carrier. The carrier often comprises iron or other metal particles. When mixed with the carrier, the toner acquires a suitable electrostatic charge so that it may easily be transferred to the photoconductive element to develop the latent electrostatic image formed thereon. Usually, a cleaning device is also installed in the electrographic printing apparatus in order to remove toner and other developer particles such as the carrier which remain on the surface of the drum or the belt after the transfer of the developed image to the sheet of recording medium. In some cases, the cleaning device is integrated into the developer unit which alternately functions in either a developing or a cleaning mode.
Heretofore, a variety of devices and methods have been used to clean residual developer particles from the photoconductive belt or drum. Thus, the cleaning device often comprises a brush which is used to remove the developer particles. The brush has a length substantially equal to the width of the photoconductive element in order that the entire photoconductive element be swept clean. The cleaning brush is formed using a suitable material to attract the toner particles, and it is positioned to face the photoconductive element so that it may contact its surface in order to remove the residual developer material.
However, cleaning brushes are not entirely satisfactory for their intended purpose. A primary requisite for effective cleaning is that the cleaning brush and the surface of the photoconductive element be constantly held in even contact. While some implementations have heretofore been proposed to satisfy this requisite, problems have been encountered with such cleaning devices in that after an extended period of use of the electrographic printing apparatus, the pressing contact of the cleaning brush with the surface of the photoconductive element becomes uneven. This tends to bring about irregularity in the cleaning operation. In order to overcome this problem, complicated devices such as that described in U.S. Pat. No. 4,571,070 (Tomita), have been proposed.
In an alternative method of cleaning the photoconductive element, a scraper blade is applied to the photoconductive element. The scraper blade, typically made from a hard rubber material, is held against the photoconductive element and scrapes it free of residual toner particles. For example, U.S. Pat. No. 4,568,175 (Inowa et al) discloses a blade cleaning device for removing toner particles remaining on the surface of a photoreceptor.
Such blade-cleaning devices are not entirely satisfactory either. First, there is the problem of maintaining the blade in even contact with the surface of the photoconductive element. Particularly as time goes by, irregularities across the width of the blade occur so that the blade is no longer maintained in even contact with the photoconductive element. Second, in many cases the blade used to clean the photoconductive element may scratch the photoconductor surface. This is particularly true when the developer material is a two component developer which includes ferrite particles. The combination of the blade and the hard ferrite particles has a tendency to scratch the sensitive surface of the photoconductive element. Third, the cleaning blade must be maintained at a fixed angle to the photoconductive element. This necessitates the use of relatively complicated structures. For example, see the structure disclosed in U.S. Pat. No. 4,568,175 (Inowa et al).
Accordingly, it is an object of the present invention to provide a cleaning device for removal of developer material from a photoconductive element which cleaning device does not suffer from the deficiencies of prior art cleaning brushes and cleaning blades.
In particular, it is an object of the present invention to provide a cleaning device for removal of developer material from a photoconductive member which is not subject to the need for high tolerances of prior art cleaning brushes and cleaning blades.
It is a further object of the present invention to provide such a cleaning device which permits recycling of the developer particles remaining on the photoconductive element.
It is a further object of the present invention to provide such a cleaning device which is simple, cheap to construct, and can be attached to a disposable photoconductive belt assembly.